This project will investigate cognitive and neural systems involved in attentional conflict and their development using functional magnetic resonance imaging (fMRI). We will examine conflict associated with the suppression of attention to salient, but irrelevant peripheral stimuli within a single task design. The task design will consist of using a variation of the classic flanker paradigm developed by Eriksen and Eriksen (1974). Congruent and incongruent flankers will be presented on either side of a target stimulus. The salience of the flankers will be manipulated by varying their predictive value such that 70% of the trials are congruent and 30% are incongruent similar to the cost benefit analysis used by Posner and Snyder (1975) to examine attention and cognitive control. The specific aims of this project are 1) to delineate cognitive and neural systems involved in attentional conflict; and 2) to further dissociate the cognitive and neural systems involved in attentional conflict developmentally in children. At least two systems have been suggested to play critical roles in resolving conflict: a) an anterior attention system including regions of the prefrontal cortex and anterior cingulate cortex; and b) a more posterior attention system involving the parietal cortex (Posner & Peterson, 1990). Furthermore, significant development in the ability to resolve conflict occurs throughout childhood. The proposed experiments will examine unique contributions of these subsystems and of regions within these subsystems in resolving conflict in children and adults using fMRI.